This proposal is to request support for a Keystone Symposia meeting entitled "Stem Cell Niche Interactions", organized by Markus Grompe, which will be held in Whistler, British Columbia, Canada from April 21 - 26, 2009. Embryonic stem cells are pluripotent precursors able to differentiate into the many cell types of the body. Adult or tissue stem cells are undifferentiated but lineage specific precursor cells able to proliferate long term while producing daughters that maintain the undifferentiated state (self-renew) and daughters that differentiate into specific cell types. In addition to their intrinsic interest for developmental biology, both kinds of stem cells have great promise for tissue renewal and regenerative medicine. Much has been learned in the past year about the mechanisms that maintain and induce stem cell pluripotency, the mechanisms that control differentiation, and the molecular regulation of stemness and self-renewal. Interactions between stem cells and their niches regulate self-renewal versus differentiation of adult stem cells and key signals from surrounding cells may organize fate decisions in space and time to pattern early embryonic development and differentiation of specific cell types. Understanding of the fundamental biology of embryonic and adult stem cells is being translated into development of "artificial niches" and conditions for controlling cell proliferation and differentiation. This meeting will bring together stem cell scientists from diverse model systems and backgrounds. All career levels will be represented. Current opportunities and challenges in the field will be highlighted in an atmosphere of informal exchange, facilitating new ideas and collaborations towards meeting the next great challenges in the field. PUBLIC HEALTH RELEVANCE: Embryonic stem cells are able to differentiate into the many cell types of the body. In addition to their intrinsic interest for developmental biology, stem cells have great promise for tissue renewal and regenerative medicine. This meeting will explore our current understanding of the biology of stem cells and their niches, the special microenvironments that dictate how stem cells operate, and whose dysfunction promotes cancer and aging.